Cellular communications systems generally support one or more cellular protocols that facilitate wireless connections between wireless devices or user equipment (UE) and cell towers operated by the cellular communications systems. Presently, these cellular communications systems are transitioning between earlier cellular protocols, such as 3G (e.g., CDMA 2000 and UMTS), and modern cellular protocols sometimes referred to as 4G long-term evolution (LTE). The modern cellular protocols support packet-switched voice and data communications over LTE, such as VoLTE, while the earlier cellular protocols involve circuit-switched cellular communications and do not support VoLTE. As the transitions occur between earlier cellular protocols as their modern counterparts, vehicle telematics units are capable of supporting both.
Unlike handheld UE, a vehicle telematics unit may not detach from a cell tower after a vehicle is turned off and the vehicle occupant leaves the vehicle. Instead, the vehicle telematics unit may remain attached to a cell tower for a week or more despite a lack of visible vehicle activity. When the vehicle telematics units are deployed in areas where the cellular communications systems only support the earlier cellular protocols, the units may camp on cell towers providing earlier cellular protocols for extended periods. Later, when the cellular communications systems begin to support the more modern cellular protocols, the vehicle telematics units may continue to use earlier protocols despite the availability of more modern cellular protocols.